Apparatus for fusing xerographic toners

ABSTRACT

A device for thermofusing an electroscopic toner image to the surface of a support by moving the support through a passageway formed by a pair of platens, at least one of which is heated. The heated platen is connected to an air supply, the air being discharged under pressure through a slot in the heated platen and directed toward the image-bearing surface. The air is heated as it is discharged and attains a temperature sufficient to fuse the toner image. The air pressure is sufficient to hold the support in a spaced relation with respect to the heated platen. In another embodiment, a vacuum platen is arranged adjacent the other surface of the support, the applied vacuum or suction drawing the thin layer of air on the image-bearing surface through the support to increase the efficiency of the device by utilizing the heated air more effectively.

United States Patent 1 3,659,348 Frank [451 May 2, 1972 [54] APPARATUSFOR FUSING FOREIGN PATENTS OR APPLICATIONS XEROGRAPHIC TONERS 542,3316/1957 Canada ..34/23 [72] Inventor; Lee F. Frank, Rochester, NY.

Primary Examiner-Carroll B. Dority, Jr.

[ Asslgnee! g i Kodak Company Rochester AttorneyW. H. .1. Kline, P. R.Holmes and L. F. Seebach 22 Filed: May 27, 1970 [57] ABSTRACT [52] U.S.Cl.. .....34/l22, 34/160, 34/162 [51] Int. Cl ..F26b 11/02 [58] FieldofSearch ..34/23, 114, 122, 155, 162, 34/160 [56] References CitedUNITED STATES PATENTS 3,403,456 10/1968 Smith ..34/162 X 3,435,7514/l969 Goodman et al.... ...34/l62 X 3,447.247 6/1969 Daane ..34/1223,098,725 7/1963 Stuchbery et al. ..34/122 X A device for thermofusingan electroscopic toner image to the surface of a support by moving thesupport through a passageway formed by a pair of platens, at least oneof which is heated. The heated platen is connected to an air supply, theair being discharged under pressure through a slot in the heated platenand directed toward the image-bearing surface. The air is heated as itis discharged and attains a temperature sufficient to fuse the tonerimage. The air pressure is sufficient to hold the support in a spacedrelation with respect to the heated platen. In another embodiment, avacuum platen is arranged adjacent the other surface of the support, theapplied vacuum or suction drawing the thin layer of air on theimagebearing surface through the support to increase the efficiency ofthe device by utilizing the heated air more effectively.

6 Claims, 3 Drawing Figures APPARATUS FOR FUSING XEROGRAPIIIC TONERSFIELD OF THE INVENTION DESCRIPTION OF THE PRIOR ART The prior artteaches that a toner image can be formed on a support bearing a latentelectrostatic image by toner particles of either the dry (powder) or wet(liquid carrier) type. Such an image can be fixed to its support orcarrier by the process of heat fusing; that is, by the application ofheat, in which case, the toner particles forming the image must be of athermoresponsive material, such as a heat fusible resin which coalescesand adheres to the surface of the support when heated and then cooled toambient temperature.

In order to fuse such a resinous toner image, it is necessary to. heatthe toner and the support, which can be paper, to which it is to befused to a relatively high temperature. For given materials, atemperature range exists in which fusing of the toner image will occur.Below such a temperature range, the resinous toner will not properlyadhere to the surface of the support. If the temperature is too high,there is a tendency for the support to discolor or scorch and, in somecases, the toner will explode or vaporize.

Various techniques have been developed for fusing, such as, oven fusing,hot air fusing, radiant fusing, hot and cold pressure roll fixing andfusing, and flash fusing. Any one of these techniques, when consideredby itself for a specific fusing application in xerography, has certainlimitations and/or deficiencies. In general, it has been difficult toachieve a completely satisfactory design for a toner fuser that willprovide a short warm-up time, low electric current requirements,adequate heat insulation and uniform heat distribution. In addition,most fusers in use at the present time also possess the disadvantagethat they cannot be readily adapted to randomly fusing images onsupports of different thickness. Specifically, a hot air oven systemtends to be slow to reach maximum heat output and requires a high powersource of potential. Hot and cold pressure systems have presentedproblems with respect to offsetting of the toner particles, resolutiondegradation, and poor retention of the toner particles.

Flash fusing has been desirable for some time because it is not onlyvery efficient at slow or intermittent reproduction speeds but alsosuitable for high speed copying. A major problem with flash fusing isthat it is not selective. Since the term selective is used in variousways in connection with fusing processes, it should be clearlyunderstood that it is herein referred to as the preferential fusing ofdense image areas leaving low density or background areas unfused.

It is well known to fuse toner particles to a support by means ofelectrically ene'rgized coils which are exposed to the toner image,although arranged in a fusing chamber, thereby providing a heatingeffect that is a combination of heat radiation and convection. When thesupport passes through the fuser at a rapid rate, the heat necessary toeffect good fusing requires extremely high coil temperatures, as well asextensive coil surface area. Thus, because of the rate of movement ofthe support, the coils are generally maintained at a temperature thatexceeds the support combustion temperature in order that fusing can beachieved within the period of time each portion of the supportissubjected to the heat. Consequently, if movement of the support shouldbe interrupted or halted, for any reason, there exists the inherentproblem of fire and/or charring of the support.

In the case of fusing with vapor or an atomized form of solvent, specialprovisions must be made to dispose of the solvent and to safeguardagainst the inherent fire hazard.

SUMMARY OF THE INVENTION One object of the present invention is toprovide a device for fusing a toner image to a support which permits thesupport to be moved at a relatively high speed and which insures fusingof the toner image to the support.

Another object of the invention is to provide a device for fusing atoner image to a support which can be available for use with arelatively short period of warm-up time and which is compatible withsupports of different thicknesses.

And yet another object of the invention is to provide a device forfusing a toner image to a support in which a very efficient transfer ofheat is obtained from a heated platen to the toner image and the uppersurface of the support.

Another object of this invention is to provide a device for fusing atoner image to a support in which an even fusing of the toner image isobtained across the entire surface of the support.

Still another object of this invention is to provide a device I forfusing a toner image to a support in which the image-bearing surface ofthe support is not in contact with any part of the fuser during thefusing operation.

Other objects and advantages of the invention will be readily apparentto those skilled in the art when the more detailed description set forthhereinbelow is read in conjunction with the attached drawing.

The aforementioned objects of the invention are attained by a device forthermofusing an electroscopic toner image to the surface of a support bymoving the support between two spaced platens, at least one of which isheated. The imagebearing surface of the support faces the heated platenwhich is provided with a transverse chamber to which an air supply isconnected by suitable ducts. The air under pressure passes through anelongated slit in said chamber, becomes heated by the platen, andmaintains the image-bearing surface of the support in a spaced relationto the facing surface of the heated platen. The successive portions ofthe toner image on the support are fused to the support by the heattransferred to the'air by the heated platen.

In one of the modifications of the aforementioned device, the platenadjacent to the other surface of the support is provided with aperforated plate with respect to which the support is moved. A suctionis applied to this platen, thereby insuring that the image-bearingsurface of the support is main- .tained in the required spaced relationwith respect to the heated platen. In this modification, the suctionalso draws the thin layer of air on the image-bearing surface of thesupport through the support, thereby rendering the heated air moreeffective.

By means of such a hot air fuser satisfactorily fused toner images canbe obtained with no smearing of the toner particles, as evidenced bywiping tests, even when the linear movement of the support between theplatens is as high as about 25 in. per second. Although air underpressure is used, the air does not disturb the toner particles on thesurface of the support or cause image smearing by displacement of tonerparticles.

DESCRIPTION OF THE DRAWING Reference is now made to the accompanyingdrawing wherein like reference numerals designate like parts andwherein:

FIG. 1 is a simplified schematic representation of a fusing deviceembodying the invention and showing the principal elements thereof;

FIG. 2 is a simplified schematic representation of another embodiment ofthe invention similar to that disclosed in FIG. 1; and

FIG. 3 is a simplified schematic representation of another embodiment ofthe invention in which the platens are provided with curved surfaces.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIG. 1, aheated platen generally designated by the numeral 10, comprises aninsulating block 13 having rectangular recesses 14 in each of which aheater 15 is arranged. Each of heaters 15 is retained in its respectiverecess by a metal plate or strip 17 which is in thermal contacttherewith. A block 18 of insulating material forms a second platengenerally designated by the numeral 19 which is arranged in spacedrelation to platen l and aligned therewith. Heater 15 can be a wire coiltype or a solid type, such as a Calrod unit. In either case,the heater15 is suitably connected to a source of potential (not shown). Platensand 19 are sufficiently wide to accommodate the maximum width of support21 that will be used in the fuser. The spaced relation of heated platen10 relative to platen 19 is such that a passageway 20 is formedtherebetween through which the support 21 can be moved at a necessaryrate to insure good fusing.

Support 21 can be moved in a preselected or defined path which includesin part the passageway 20 between heated platen l0 and platen'l9. Inthis portion of the path, support 21 is moved by a porous mesh belt 23which encircles'pulleys 25 and 29, one of which serves to drive belt 23from a suitable drive means such as a motor 26 which is showndiagrammatically in FIG. 1 as being connected to pulley 25. Support 21is carried by the belt 23 with the surface S,.that is, the imagebearingsurface, being orientated toward heated platen 10. Support 21 is meanttoinclude those materials used in the field of electrophotography whichare capable of retaining a toner image on a surface thereof by means ofan electrostatic charge corresponding to the image. Such. materials caninclude paper, dielectric materials, materials coated with aphotoconductive material, etc. Also, such materials can be in theform'of discrete sheets or a continuous web. In any case, the fusingoperation is usually the last step in a series of well known steps forattaining a usable toner image.

A flow of air under pressure is introduced into a chamber 22 in platen10 and directed to surface S of carrier 21 by a slot 24 that extendstransversely of'platen l0 and support 21 with respect to its directionof movement. Chamber 22 is connected by line 27 to a blower 28. The airintroduced into chamber 22 by blower 28 through line 27 can only exitthrough slot 24 which is sufficiently long so as to extend across thewidth of the support 21. Slot 24 is closed at its ends so that the airmust exit through slot 24 and be directed at surface S. The air pressureis sufficient to maintain surface S in spaced relation to plates 17 onheated platen 19 without disturbing the toner image. As discussedhereinafter, an air space between the facing surfaces of plates 17 andsurface S of support 21- is of such size that substantially no airturbulence exists in this space. Hence, the toner image is not molestedor disarranged in any way.

Since the toner image on surface S of support 21 must be heated to atemperature to fuse the toner particles to the support withoutoverheating the support itself, the support is introduced into thepassageway 20 between platens 10 and 19 so that surface S faces platen10. In the form that support 21 with its tonerimage is introduced, thetoner particles are adhered to surface S only by the electrical fieldexisting between the charged particles and the charge inthe image areas.As a result, the image-bearing surface is preferably not in contact withany other surface prior to fusing of the image.

The thermal conductivity of the air space between the facing surfaces ofplates 17 and support 21 increases as the thickness of the air spacedecreases. The thermal conductivity will also increase as the amount ofshear in this space decreases, shear being defined (approximately) asthe average air velocity in thespace divided by the thickness (distanceas measured from facing surface of plate 17 to surface S or to facingsurface of belt 23) of the space. These two effects combine to produce avery noticeable increase in thermal conductivity with a decreasingthickness in air space. In addition, less air is required with thesmaller spacings to maintain the shear. As a result, with a 0.005 inchspacing between the facing surfaces of plates 17 and support 21 it hasbeen found that more heat is transferred to the support 21 than istransferred to the exhausting air. Such very high thermal conductivitypermits operation without risk of charring support 21 because the heatpresented by plates 17 is used so efficiently that an excessivetemperature does not have to be generated by heaters 15, therebynegating any charring risk. The dimension of 0.005 inch spacing can beincreased to about 0.020 inch before any great difference in thermalconductivity can be noted. Beyond this point, the heat transferfalls offconsiderably. As a result, support 21 can be moved through passageway 20at a relatively high rate of speed with completely satisfactory fusingof the toner image to support 21. a

Metal plates or strips 17 can bemade of a metal having a high thermalconductivity and low heat capacity. This allows the temperature ofplates 17 to rapidly reach a required temperature when heaters 15 areenergized.

FIG. 2 shows an embodiment of the invention in which a vacuum platen 31comprising a chamber 32 covered with a plate 33 having a configurationof holes 34, as is well known in the art, is arranged in spaced relationto platen 10. Chamber 32 is connected to a vacuum pump 35 by a duct 36.Support 21 is positioned on and moved'by belt 23 with surface S, thetoner image-bearing surface facing heated platen 10, as described abovewith respect to FIG. 1. Also, the spacing between platens 10 and 31 issuch as to provide passageway 20 for belt 23 and support 21 with thedistance between the facing surfaces of plates 17 and support 21 beinggenerally the same as set forth above. Support 21 is maintained inposition on belt 23 by the combined action of the air under pressurebeing discharged through slot 24 in heated platen 10 and the vacuumbeing applied through holes 34 in platen 31.

Another advantage obtained by using vacuum platen 31 is that when usingnormal paper for the making of copies, there is a thin layer of airwhich is maintained at surface S of support 21 which decreases thecapability of the unit to properly fuse. The slight reduced pressureapplied to the back of support 21 by vacuum platen 31 draws this layerof air through the paper, thus increasing the thermal conductivity aswell as the efficiency of the fusing device.

The device shown in FIG. 2'produces satisfactory fusing with a vacuum inplaten 31 in the range between 0.0 and 1.2 inches of mercury. The gapbetween plates 17 and the surface S of the support 21 can be in therange between approximately 0.002 inches to about 0.022 inches for asatisfactory operation. The fusing temperature, or hot air temperaturemust be maintained below 400 C to insure that the support does not charor otherwise deteriorate. Satisfactory fusing has been obtained with thesupport 21 being moved at the rate of approxi mately 10 to 25 inches persecond, the rate being dependent on the type of support and itsthickness.

It should be understood that the specific embodiments of the presentinvention described hereinabove have been described to facilitate adisclosure of the invention rather than to limit the particular formwhich the invention might assume. For example, support 21 can be'movedthrough passageway 20 between platens 19 and 21 by any suitable meanswell known in the art for moving a sheet or a web at a generallyconstant speed. In addition, a perforated metal drum 40 can be used inplace of vacuum platen 31 and/or porous mesh belt 23 as shown in FIG. 3,the parts corresponding to those in FIGS. 1 and 2 being indicated by thesame numeral with a prime symbol. Also, after the air being dischargedfrom slot 24 in heated platen 10 passes over surface S of support 21, itcan be recycled to increase the efficiency of the fusing device.Furthermore, vacuum platen 31 can also be heated to increase theefficiency of the device.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

1 claim:

1. A device for fusing an electroscopic toner image to the surface of asupport bearing said toner image, comprising:

two platens having spaced, opposed surfaces, at least one of saidplatens having a central chamber and being heated and provided with anelongated slot interconnecting said chamber to the heated surfacethereof facing the image bearing surface;

means for moving said support between said opposed surfaces in adirection transverse of said slot with said imagebearing surface facingthe heated surface of said one platen;

means operatively associated with said heated platen for directing aflow of air under pressure into said chamber for discharge through saidslot into the space between said opposed surfaces and at saidimage-bearing surface to maintain the latter in spaced relation to theheated surface of said one platen;

said flow of air between said opposed surfaces transferring sufficientheat from the heated surface of said one platen to said image-bearingsurface to fuse said toner image to said support.

2. The fusing device in accordance with claim 1 wherein said heatedplaten is provided with one or more heating elements on each side ofsaid chamber and adjacent the facing surface of said heated platen..

3. The fusing device in accordance with claim 1 wherein the other ofsaid platens comprises a hollow, rotatable drum having a perforatedperipheral surface for engaging the other surface of said support atleast along a line generally opposite and aligned with said elongatedslot.

4. The fusing device in accordance with claim 3 including vacuum meansconnected to said drum for maintaining the other surface of said supportagainst the peripheral surface of said drum.

5. The fusing device in accordance with claim 1 wherein the spacebetween the image-bearing surface of said support and the facing surfaceof said heated platen is from 0.005 to about 0020 inches.

6. The fusing device in accordance with claim 4 wherein said vacuummeans draws the thin layer of air on said imagebearing surface throughsaid support, thereby rendering more effective the heat transfer fromsaid heated platen to said image-bearing surface by said flow of air.

1. A device for fusing an electroscopic toner image to the surface of asupport bearing said toner image, comprising: two platens having spaced,opposed surfaces, at least one of said platens having a central chamberand being heated and provided with an elongated slot interconnectingsaid chamber to the heated surface thereof facing the image-bearingsurface; means for moving said support between said opposed surfaces ina direction transverse of said slot with said image-bearing surfacefacing the heated surface of said one platen; means operativelyassociated with said heated platen for directing a flow of air underpressure into said chamber for discharge through said slot into thespace between said opposed surfaces and at said image-bearing surface tomaintain the latter in spaced relation to the heated surface of said oneplaten; said flow of air between said opposed surfaces transferringsufficient heat from the heated surface of said one platen to saidimage-bearing surface to fuse said toner image to said support.
 2. Thefusing device in accordance with claim 1 wherein said heated platen isprovided with one or more heating elements on each side of said chamberand adjacent the facing surface of said heated platen.
 3. The fusingdevice in accordance with claim 1 wherein the other of said platenscomprises a hollow, rotatable drum having a perforated peripheralsurface for engaging the other surface of said support at least along aline generally opposite and aligned with said elongated slot.
 4. Thefusing device in accordance with claim 3 including vacuum meansconnected to said drum for maintaining the other surface of said supportagainst the peripheral surface of said drum.
 5. The fusing device inaccordance with claim 1 wherein the space between the image-bearingsurface of said support and the facing surface of said heated platen isfrom 0.005 to about 0.020 inches.
 6. The fusing device in accordancewith claim 4 wherein said vacuum means draws the thin layer of air onsaid image-bearing surface through said support, thereby rendering moreeffective the heat transfer from said heated platen to saidimage-bearing surface by said flow of air.